Mathematical ability is highly linked to earning power and career success. A new paper in Current Biology demonstrates that six days of 20 minute sessions of electrical stimulation over the parietal lobe can increase some numerical literacy tasks, even six months after the stimulation was applied!

The electrical stimulation is called transcranial direct-current stimulation (TDCS). In this paradigm, electrodes are placed on the scalp as in EEG, and then a small amount of current (1-2 mA) is applied. In this paper, electrodes were applied to the parietal lobe as injuries to this region can lead to numerical difficulties. Three groups of participants were tested: two experimental groups who received stimulation, with the current going in each direction, and a control group who had electrodes applied, but without electrical stimulation (sham stimulation).

During the stimulation, participants were presented with pairs of novel symbols that stood for digits. Participants would learn the value of these symbols by indicating which symbol represented the larger value.

As you can see from this figure, all three groups learned the task over the six experimental sessions.

Following the learning task, participants would then be given a "numerical Stroop" task to determine the automaticity of the symbol-value relationships. In this task, pairs of symbols are presented with one larger than the other. The larger symbol could be the symbol representing the larger value (congruent condition), could be the same value as the smaller value (neutral condition), or the larger symbol could represent the smaller value (incongruent condition). If the newly learned symbols were being processed as numbers, then the reaction times in the incongruent condition should be longer than neutral while congruent trials should lead to faster reaction times.

It turns out that the stimulation did lead to an increased congruity effect, but only when the current was going in one direction (right-annode, left-cathode). In fact, current in the opposite direction seemed to decrease the learning of the symbols!

As illustrated in the left-hand figure, sham stimulation led to a ~65ms congruency effect (because even without stimulation, the participants were still learning the task). However, in the right-annode, left-cathode stimulation, the effect was about twice as large, while the opposite stimulation provided no learning at all.

Over at Practical Ethics, this paper is being discussed in terms of the societal benefit that could come from increased mathematical ability. Indeed, increasing numerical literacy could indeed decrease poverty and lead to increased innovation as they suggest. I also agree with their general unease about the possibility of "anti-enhancement" of mathematical abilities that is suggested from the right-cathode stimulation condition.